A mobile communication terminal such as a cellular phone modulates quadrature baseband signals I and Q for transmission. A local oscillator supplies a frequency used for the modulation via an image rejection mixer.
In Europe, for example, a cellular phone is requested for transmission correspondingly to different communication systems such as GSM, DCS, PCS, and UMTS. These communication systems use different frequencies for transmission. Consequently, the local oscillator and the image rejection mixer are needed for each communication system.
However, providing each communication system with the local oscillator and the image rejection mixer may increase the circuit scale of the mobile communication terminal.
It is therefore an object of the present invention to provide a communication apparatus having a small-scale circuit used for modulation.